Stellar explosions powered by the Blandford-Znajek mechanism

In this letter we briefly describe the first results of our numerical study on the possibility of magnetic origin of relativistic jets of long duration gamma ray bursters within the collapsar scenario. We track the collapse of massive rotating stars onto a rotating central black hole using axisymmetric general relativistic magnetohydrodynamic code that utilizes a realistic equation of state of stellar matter, takes into account the cooling associated with emission of neutrinos, and the energy losses due to dissociation of nuclei. The neutrino heating is not included. We describe the solution for one particular model where the progenitor star has magnetic field $B=10^{10}$G. The solution exhibits strong explosion driven by the Poynting-dominated jets whose power exceeds $2\times10^{51} {erg/s}$. The jets originate mainly from the black hole and they are powered via the Blandford-Znajek mechanism. The full details of the simulations together with the results of parameter study will be presented elsewhere. A number of simulation movies can be downloaded from http://www.maths.leeds.ac.uk/~serguei/research/movies/anim.htmlComment: minor revision, accepted by MNRAS Letters, simulation movies can be downloaded from http://www.maths.leeds.ac.uk/~serguei/research/movies/anim.htm

Preliminary results of investigation of solid interplanetary matter in the vicinity of the moon

Density of matter near moon found to be greater than that of interplanetary spac

1245+676 - a CSO/GPS source being an extreme case of a double-double structure

AGN with the so-called `double-double' radio structure have been interpreted as restarted AGN where the inner structure is a manifestation of a new phase of activity which happened to begin before the outer radio lobes resulting from the previous one had faded completely. The radio galaxy 1245+676 is an extreme example of such a double-double object - its outer structure, measuring 970 h^{-1} kpc, is five orders of magnitude larger than the 9.6 h^{-1} pc inner one. We present a series of VLBI observations of the core of 1245+676 which appears to be a compact symmetric object (CSO). We have detected the motion of the CSO's lobes, measured its velocity, and inferred the kinematic age of that structure.Comment: A contribution to The Third Workshop on Compact Steep Spectrum and GHz-Peaked Spectrum Radio Sources, Kerastari, Greece May 28-31, 2002. Refereed and accepted by Publications of the Astronomical Society of Australia. 4 pages. Final version copyedited by PASA Edito

Polarization in the inner region of Pulsar Wind Nebulae

We present here the first effort to compute synthetic synchrotron polarization maps of Pulsar Wind Nebulae (PWNe). Our goal is to highlight how polarization can be used as an additional diagnostic tool for the flow structure in the inner regions of these nebulae. Recent numerical simulations suggest the presence of flow velocities ~0.5 c in the surroundings of the termination shock, where most of the high energy emission comes from. We construct polarization maps taking into account relativistic effects like Doppler boosting and position angle swing. The effect of different bulk velocities is clarified with the help of a toy-model consisting of a uniformly emitting torus. We also present a map based on recent numerical simulations of the entire nebula and compare it with presently available data. The comparison with upcoming high resolution observations could provide new insight into the inner structure of the nebula and put constraints on the geometrical properties of the magnetic field.Comment: Accepted for publication on A&A, 6 pages, 2 figure

Understanding possible electromagnetic counterparts to loud gravitational wave events: Binary black hole effects on electromagnetic fields

In addition to producing loud gravitational waves (GW), the dynamics of a binary black hole system could induce emission of electromagnetic (EM) radiation by affecting the behavior of plasmas and electromagnetic fields in their vicinity. We here study how the electromagnetic fields are affected by a pair of orbiting black holes through the merger. In particular, we show how the binary's dynamics induce a variability in possible electromagnetically induced emissions as well as an enhancement of electromagnetic fields during the late-merge and merger epochs. These time dependent features will likely leave their imprint in processes generating detectable emissions and can be exploited in the detection of electromagnetic counterparts of gravitational waves.Comment: 12 page

Simulated synchrotron emission from Pulsar Wind Nebulae

A complete set of diagnostic tools aimed at producing synthetic synchrotron emissivity, polarization, and spectral index maps from relativistic MHD simulations is presented. As a first application we consider here the case of the emission from Pulsar Wind Nebulae (PWNe). The proposed method is based on the addition, on top of the basic set of MHD equations, of an extra equation describing the evolution of the maximum energy of the emitting particles. This equation takes into account adiabatic and synchrotron losses along streamlines for the distribution of emitting particles and its formulation is such that it is easily implemented in any numerical scheme for relativistic MHD. Application to the axisymmetric simulations of PWNe, analogous to those described by Del Zanna et al. (2004, A&A, 421, 1063), allows direct comparison between the numerical results and observations of the inner structure of the Crab Nebula, and similar objects, in the optical and X-ray bands. We are able to match most of the observed features typical of PWNe, like the equatorial torus and the polar jets, with velocities in the correct range, as well as finer emission details, like arcs, rings and the bright knot, that turn out to arise mainly from Doppler boosting effects. Spectral properties appear to be well reproduced too: detailed spectral index maps are produced for the first time and show softening towards the PWN outer borders, whereas spectral breaks appear in integrated spectra. The emission details are found to strongly depend on both the average wind magnetization (here approximately 2%), and on the magnetic field shape.Comment: 14 pages, submitted to A&

Jet Formation in the magnetospheres of supermassive black holes: analytic solutions describing energy loss through Blandford-Znajek processes

In this paper, we provide exact solutions for the extraction of energy from a rotating black hole via both the electromagnetic Poynting flux and matter currents. By appropriate choice of a radially independent poloidal function $\Lambda(\theta)$, we find solutions where the dominant outward energy flux is along the polar axis, consistent with a jet-like collimated outflow, but also with a weaker flux of energy along the equatorial plane. Unlike all the previously obtained solutions (Blandford & Znajek (1977), Menon & Dermer (2005)), the magnetosphere is free of magnetic monopoles everywhere

3C454.3 reveals the structure and physics of its 'blazar zone'

Recent multi-wavelength observations of 3C454.3, in particular during its giant outburst in 2005, put severe constraints on the location of the 'blazar zone', its dissipative nature, and high energy radiation mechanisms. As the optical, X-ray, and millimeter light-curves indicate, significant fraction of the jet energy must be released in the vicinity of the millimeter-photosphere, i.e. at distances where, due to the lateral expansion, the jet becomes transparent at millimeter wavelengths. We conclude that this region is located at ~10 parsecs, the distance coinciding with the location of the hot dust region. This location is consistent with the high amplitude variations observed on ~10 day time scale, provided the Lorentz factor of a jet is ~20. We argue that dissipation is driven by reconfinement shock and demonstrate that X-rays and gamma-rays are likely to be produced via inverse Compton scattering of near/mid IR photons emitted by the hot dust. We also infer that the largest gamma-to-synchrotron luminosity ratio ever recorded in this object - having taken place during its lowest luminosity states - can be simply due to weaker magnetic fields carried by a less powerful jet.Comment: 19 pages, 3 figures, accepted for publication in Ap

Relativistic MHD Simulations of Jets with Toroidal Magnetic Fields

This paper presents an application of the recent relativistic HLLC approximate Riemann solver by Mignone & Bodo to magnetized flows with vanishing normal component of the magnetic field. The numerical scheme is validated in two dimensions by investigating the propagation of axisymmetric jets with toroidal magnetic fields. The selected jet models show that the HLLC solver yields sharper resolution of contact and shear waves and better convergence properties over the traditional HLL approach.Comment: 12 pages, 5 figure